Damping foil consisting of several layers and a method for producing same

ABSTRACT

A multi-layer damping foil having a perforated lower layer facing towards a part to be damped, with properties which are suitable for adhering the damping foil onto the part. A non-perforated upper layer, facing away from the part, does not have adherence properties. Advantageously there may be provided between the upper and lower layers a thin film-like intermediate layer of non-woven fabric, kraft paper, or the like, which may have openings.

This is the U.S. national phase of International Application No.PCT/EP01/00499 filed Jan. 17, 2001, the entire disclosure of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a multi-layer damping foil or anti-drummingfoil.

2. Description of Related Technology

Damping foils or anti-drumming foils are employed, in particular in theautomobile industry, for the sound deadening, i.e. sound damping, ofsheets or panels. In particular, such damping foils can be placed in theinterior roof and side regions of a body and there adhere firmly allover the surface. Frequently, such damping foils are painted over. Theall-over surface adherence is attained, in accordance with the state ofthe art, in that the side of the damping foil towards the sheet or panelto be damped is provided with a hot-melt glue and after application ofthe damping foil onto the sheet to be damped a heat treatment is carriedout which brings about the melting of the hot-melt glue and therewithattains the all-over surface gluing. In order to be able to hold thedamping foil in position before the heat treatment, in particular in thecase of roof and side regions of a body, in accordance with the state ofthe art such a damping foil is constituted to be magnetisable. For thispurpose, previously, rod or strip-shaped metal parts have been set intothe side of the damping foil towards the sheet to be damped (DE 38 25494 A1) or there are mixed into the damping foil, in its production,ferrite powder or similar magnetic or magnetisable powdery particles (DE34 27 916 A1). Damping foils constituted in this way adhere during theheat treatment to the body sheeting due to their own magneticproperties, or due to permanent magnets arranged on the outer side ofthe sheeting, which attract the magnetisable particles in the dampingfoil and therewith the entire damping foil. After it had been determinedthat it was sufficient to correspondingly constitute only a certainlayer thickness, it was proposed to employ a multi-layer structure withwhich a lower layer, towards the sheet or panel, contains magnetic ormagnetisable particles and that a layer away from the sheet or panel,which layer fulfils in substance the damping function, does not needsuch particles. Between these layers, both in general includingbituminous material, there can be embedded, in accordance with the stateof the art, a flexible foil of aluminium or polyethylene (EP 0 285 740B1).

In particular the layer towards the sheet to be damped, having themagnetic or magnetisable particles, has high mass per unit area and thusdetermines the overall weight of the damping foil to be applied to avery significant degree, without this layer contributing significantlyto the damping.

SUMMARY OF THE INVENTION

Starting from here, it is the object of the invention to improve adamping foil as explained above to the effect that without adverselyeffecting the sound damping behaviour and the readiness of applicationto the part to be damped, the mass per unit area is reduced.

This object is achieved in accordance with the invention in that thelower layer, towards the part to be damped, such as a body sheet, hasnumerous through-openings in the sense of being perforated.

Of particular advantage, with regard to acoustic properties, is toprovide between the two layers an intermediate layer of non-woven fabricor kraft paper.

With a particular configuration for certain production technologies itis expedient to provide these openings not only in the lower layer butalso in the associated intermediate layer, such that the material of theupper layer upon its application can penetrate through the openings.Even if the mass per unit area of the lower layer is thereby slightlyincreased in comparison with a configuration in which the openings arefilled with air, the damping foil can however be produced overall moreeconomically, since the material of the upper layer can be applied tothe lower layer, provided with the intermediate layer, in a simplemanner and bonds very well with lower layer and intermediate layer.

Alternatively, the lower layer can be formed also as adhesive layerwhich whilst achieving an adherent connection is removable intact, as isper se known from DE 35 10 932 A1 or EP 0 195 923 B1.

In the production of a damping foil in accordance with the invention, ona web or sheet material forming the lower layer, after perforationthereof, a web or sheet material forming the upper layer is laminated onor applied in some other manner. If an intermediate layer is providedthis is to be laminated onto the lower layer before or after theperforation of that layer. For example, the non-woven fabric or thekraft paper which forms intermediate layer may be constituted to beadhesive on both sides.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail with reference to theexemplary embodiments illustrated in the drawings. There is shown:

FIG. 1 in an exploded and perspective illustration, a section of adamping foil in accordance with the invention viewed towards the sidefacing the part to be damped,

FIG. 2 in section, a damping foil, laid on a sheet to be damped, inaccordance with a first exemplary embodiment,

FIG. 3 in section, a damping foil, laid on a sheet to be damped, inaccordance with a second exemplary embodiment,

FIG. 4 in section, a damping foil, laid on a sheet to be damped, inaccordance with a further exemplary embodiment,

FIG. 5 the temperature dependence of the loss factor, determined inaccordance with a bending vibration test, of an exemplary embodiment ofdamping foil in accordance with FIG. 2.

DETAILED DESCRIPTION

FIG. 1 shows in perspective and in exploded illustration a damping foil2 viewed towards the side 13, facing the part to be damped, of a “lower”layer 3, facing the part to be damped, of the damping foil 2. Thedamping foil 2 further has “upper” layer 4, facing away from the part tobe damped, and a film-like intermediate layer 5, formed by means ofnon-woven fabric or by means of kraft paper, between the layers 3 and 4of the damping foil 2. On the side 13 facing the part to be damped theremay be applied an adhesive such as a hot-melt glue 12 or a dispersionglue. The lower layer 3 of the damping foil 2 is formed, at least in theregion of this side 13, as an element attaining at least a temporaryadherent connection with the part to be damped. In accordance with afirst exemplary embodiment there are embedded in the material of thelower layer 3 magnetised or magnetisable particles (for examplefollowing DIN 17470 and DIN 50470), in the following briefly referred toas ferrite powder.

For weight reduction this lower layer 3 has openings 7, of which a feware iIllustrated. These openings are expediently formed for simpleproduction in the manner of perforations penetrating through the entirelower layer 3. Further, impressions 11 are advantageously provided inthe side 13 of the lower layer 3, which are so arranged that theyconnect the openings 7. They serve, in the heat treatment for activatingthe hot-melt glue 12, to prevent that air inclusions remain between thepart to be damped and the side 13 of the layer 3. The surface pattern ofthe impressions 11 is thereby not restricted to the pattern illustratedin FIG. 1. A significant factor is that the impressions 11 are providedfor each of the openings 7,

The void proportion of the openings 7 amounts expediently to about 5 to30% of the lower layer 3. Expediently, the lower layer 3 has a thicknessof from 0.2 to 1.2 mm, preferably from 0.5 to 1 mm and is of a bitumenor a bitumen mixture with a ferrite powder component amounting to about50 to 70 weight percent. The upper layer 4 of the damping foil,containing no such magnetic or magnetisable particles, and away from thepart to be damped, is about 0.8 to 2 mm thick and is expedientlylikewise of bitumen or a bitumen mixture. This upper layer 4 is fixedlybonded with the lower layer 3 having the openings 7, for example bymeans of gluing or lamination. For reasons of acoustics it is ofsignificant advantage to provide between these two layers 3 and 4 a thinintermediate layer 5 of nonwoven fabric or kraft paper. The thickness ofthis intermediate layer 5 is of the order of 0.1 mm. It may be laminatedor glued onto the lower layer 3, onto which in turn the upper layer 4 islaminated or glued. Of advantage is an intermediate layer 5 constitutedto be adhesive on both sides. As explained below with reference to FIG.2 and FIG. 4, the intermediate layer 5 may be continuous (FIG. 2) or maylikewise have openings 8 (FIG. 4).

The side 14 of the upper layer 4 of the damping foil 2 away from thepart to be damped is the so-called “sight side”, which in manyapplications, in particular in the damping of body panels, is paintedover. It may thus expediently have a further cover layer 6 (FIG. 2 andFIG. 3), which stabilises the long-term behaviour of this sight side 14.The cover layer 6 can be formed by a per se known antiblocking coating,for avoiding blocking during transportation or storage, or can also beformed by a dispersion coating in order to reduce the externally visibleeffect oyellowing in the case of light coloured paints. This cover layer6 is, however, not necessary if there is no reason to fear a risk ofblocking or a risk of yellowing.

FIG. 2 shows the application of the damping foil 2 onto a part to bedamped, in particular a sheet 1. With the exemplary embodiment inaccordance with FIG. 2 there is provided an intermediate layer 5 whichis not perforated. By these means it is prevented that material of theupper layer 4 can enter into the openings 7, which could arise under theeffect of heat, this sinking then possibly being visible in the sightside 14 directed outwardly. This exemplary embodiment is then ofparticular advantage if the two layers 3 and 4 are to be produced as webor sheet material and then laminated onto one another.

Another manner of production is however conceivable, namely that withthe layer 3, produced as web or sheet material with openings 7 providedtherein, the material forming the layer 4 is directly applied such thatit can penetrate complete or partly into the openings 7, which isillustrated by means of the stopple-like penetrations 9. By these meansan extremely good, firm connection between the two layers 3 and 4 isensured. This is illustrated in more detail in FIG. 3. In order to beable, to attain the generally desired high loss factor, here also it isexpedient to provide an intermediate layer 5. In order likewise to beable to attain penetrations, it is expedient also to provide theintermediate layer 5 with corresponding openings 8, which align with theopenings 7 in the lower layer 3. It is however in no sense urgentlyrequired that all openings 7 in the lower layer 3 align with therespective associated openings 8 in the intermediate layer 5. This isnecessary merely to the extent that firm connection between lower layer3 and upper layer 4 is ensured. Thereby it is to be taken intoconsideration that the penetrations 9 have higher weight than the airinclusions in the openings 7 in the embodiment according to FIG. 2.

In FIG. 2 the ferrite powder particles which bring about the magnetic ormagnetisable properties of the upper damping foil 2 are represented bypoints 10. By ferrite powder particles there should be merely understoodinclusions which can attain the desired effect, namely the adhering ofthe damping foil 2 to the sheet 1 to be damped, at least during the heattreatment after the application of the damping foil 2 onto the sheet 1for the attainment of the firm connection by means of a hot-melt glue,as is explained above. This adhesion can be effected by means of themagnetic properties of these particles 10 themselves, or by means of thecapability to cooperate with permanent magnets provided on the otherside of the sheet 1.

This (as a rule only temporary) adhesion can however also be broughtabout completely or in part by means of per se known so-called adhesiveconstituting of the lower layer 3. This adhesive constituting, whichpermits an adherent wide area connection of the damping foil 2 with thesheet 1, whereby however the damping foil 2 can be again removedcompletely intact, is in particular attained in that the layer on theside 13 towards the sheet 1, or in the section neighbouring thereto, hasa layer structure of a strongly deficiently cross-linked polyurethane.With bitumen, in particular blown bitumen, this is attainable by meansof the mixing of an atactic propylene in a proportion of atacticpolypropylene to bitumen of about 1:3. In the mixing of the material forthe lower layer 3 the viscosity in the melt at 180° C. is advantageouslyabout 50,000 mPa.s and more, with a penetration value in accordance withDIN1995 between 15 and 55, preferably 35 and 55.

To make more clear the sound-damping function of the damping foil 2,FIG. 5 shows the result of a bending vibration test, measured inaccordance with DIN 53440 at a frequency of 200 Hz.

In accordance with the invention it is also possible that the lowerlayer 3 is both constituted to be adhesive and also provided withferrite particles.

With regard to the weight saving that can be achieved it should be notedthat conventional single-layer or double-layer damping foils, whichattain a loss factor of more than 0.1 at 0° C. to 35 . . . 40° C., havea weight per unit area which is 5 kg/m² and more. With application ofthe present inventions these weights per unit area overall can bereduced significantly, to about 4.2 kg/m² and less.

1. A multi-layer damping foil comprising a perforated first layer toface a part to be damped, said first layer having properties suitablefor adhering the damping foil onto the part, and a non-perforated secondlayer to face away from the part, wherein said second layer does nothave such adherence properties.
 2. The multi-layer damping foilaccording to claim 1, wherein the first layer has, on a side to face thepart, impressions which connect the perforations with one another. 3.The multi-layer damping foil according to claim 1, further comprising athin, film-like intermediate layer disposed between the first and secondlayers.
 4. The multi-layer damping foil according to claim 3, whereinthe intermediate layer has openings which align with the perforations inthe first layer.
 5. The multi-layer damping foil according to claim 3,wherein the intermediate layer is a non-woven fabric layer or kraftpaper layer.
 6. The multi-layer damping foil according to claim 3,wherein the intermediate layer is provided on both sides with a gluelayer, for connection with the first and second layers.
 7. Themulti-layer damping foil according to claim 1, wherein the first layerhas a void proportion of about 5 percent to about 30 percent.
 8. Themulti-layer damping foil according to claim 1, wherein the first layercontains magnetic or magnetizable particles.
 9. The multi-layer dampingfoil according to claim 8, wherein the particles are present in aproportion of about 50 weight percent to about 70 weight percent. 10.The multi-layer damping foil according to claim 1, further comprising adispersion glue layer or a hot-melt glue layer on a side facing thepart.
 11. The multi-layer damping foil according to claim 1, furthercomprising a dispersion coating, an antiblocking coating or anothersurface covering layer on a side facing away from the part.
 12. Themulti-layer damping foil according to claim 1, wherein at least one ofthe first and second layers comprises a bituminous material.
 13. Themulti-layer damping foil according to claim 1, wherein the first layerhas a thickness of about 0.3 mm to about 1.2 mm, and the second layerhas a thickness of about 0.8 mm to about 2 mm.
 14. The multi-layerdamping foil according to claim 1, wherein the damping foil is sodimensioned that a loss factor thereof is more than 0.1 at 0° C. to 40°C., and the mass per unit area is less than 5 kg/m².
 15. The multi-layerdamping foil according to claim 1, wherein at least a portion of thefirst layer has a layer structure of a strongly deficiently cross-linkedpolyurethane.
 16. The multi-layer damping foil according to claim 15,wherein the first layer is a bituminous mixture.
 17. The multi-layerdamping foil according to claim 16, wherein the mixture has a meltviscosity at 180° C. of at least about 50000 mPa·s and a penetrationvalue according to DIN 1995 between 15 and
 55. 18. A method forproducing a multi-layer damping foil comprising a perforated first layerto face a part to be damped, said first layer having properties suitablefor adhering the damping foil onto the part, and a non-perforated secondlayer to face away from the part, wherein said second layer does nothave such adherence properties, the method comprising the steps of:producing a first layer, perforating the first layer to form openingsthrough the first layer, and applying a further, second layer onto thefirst layer.
 19. The method according to claim 18, comprising applying,before or after the perforating step, a thin, flexible intermediatelayer onto the first layer.
 20. The method according to claim 18,comprising embossing depressions into the first layer on a side thereofaway from the second layer after the application thereof, such thatthese depressions connect the openings with one another.
 21. Themulti-lever damping foil according to claim 13, further comprising afilm-like intermediate layer disposed between the first and secondlayers, the intermediate layer having a thickness of about 0.1 mm. 22.The multi-lever damping foil according to claim 14, wherein the mass perunit area is less than about 4.2 kg/m².
 23. The multi-layer damping foilaccording to claim 16, wherein the first layer is a mixture of blownbitumen and atactic polypropylene.
 24. The multi-layer damping foilaccording to claim 23, wherein atactic polypropylene and blown bitumenare present in the mixture in a ratio of atactic polypropylene tobitumen of about 1:3.
 25. The multi-layer damping foil according toclaim 17, wherein said penetration value is between 35 and
 55. 26. Themethod according to claim 18, comprising laminating the second layeronto the first layer.
 27. The method according to claim 19, comprisinglaminating the intermediate layer onto the first layer.